1. Technical Field
The present invention relates to a modem which permits the exchange of digital data with a remote modem, and more particularly, relates to an especially designed reset circuit for a modem with a variety of additional functions such as facsimile function, voice function, or combined facsimile and voice function, etc.
2. Related Art
Conventional modem is known as a data communication adapter comprising a modulator-demodulator for telephone network communication between data terminals such as computer systems. Exemplary configurations are disclosed, for example, in U.S. Pat. No. 4,085,449 for Digital Modem issued to Walsh, and U.S. Pat. No. 4,811,358 for Subscriber Line Interface Modem issued to Smedley et al. Modems for personal computer applications are currently available in two general types: (1) an internal modem typically contained on a single printed circuit board and adapted to be inserted into an expansion slot providing within the computer housing such as disclosed in U.S. Pat. No. 5,134,648 for Reconfigurable Modem For A Computer Or The Like issued to Hochfield; and (2) an external modem having its own power supply and connected to an input/output (I/O) port of the computer.
Generally, modem is intended for data communication between computer systems such that a separate reset circuit is not included to reset the modem for different data transfer rates so as to minimize production cost. Usually, internal modem is conveniently disposed within the computer housing and need not include its own power supply. However, it has disadvantages in that it provides no visual display of modem activity and requires that the entire computer including the modem be shut down and rebooted in the case of a modem jam. In contrast, the external modem includes one or more indicators displaying the modem activity and is provided with a separate on/off control switch for turning on/off the modem independently from the computer so that the modem can be rebooted separately from the computer in case of a modem jam. The disadvantages of the external modem is that it requires the provision of an AC adapter, external cabling for connection to the computer and an extra serial I/O port even when not in use. Recent efforts such as disclosed in U.S. Pat. No. 5,050,041 for Modem Mountable In Wall Of A Computer Housing With Readily Accessible On/Off Switch Connecting Either Modem Or An Auxiliary Serial Port To An I/O Port issued to Shafi, have been made to provide a hybrid configured modem suitable for mounting in a computer slot but retaining communication indicators and an on/off switch that is readily accessible to the user. No reset circuit is, however, provided to reset operation of the modem. U.S. Pat. No. 5,828,697 for Modem Having External Reset Circuit issued to Seong-Kee Shin discloses a reset circuit for a modem only.
Recent advanced modem having multiple modem functions including a facsimile function, a voice function, a simultaneous voice and data function (SVD) in addition to the original digital data exchange function, however, requires some reset schemes for initializing operation of the modem for the exchange of digital data in one of a basic modem mode and an additional modem mode at different data transfer rates. Examples of such a modem are disclosed in U.S. Pat. No. 5,295,156 for Modem issued to Heep et al., U.S. Pat. No. 5,384,780 for High Speed Modem, Method And System For Achieving Synchronous Data Compression issued to Lomp, and U.S. Pat. No. 5,537,654 for System For PCMCIA Peripheral To Execute Instructions From Shared Memory Where The System Reset Signal Causes Switching Between Modes Of Operation By Alerting The Starting Address issued to Bedingfield. In Bedingfield '654, for example, the subscriber line interface modem is reset in response to a reset signal generated from the computer's CPU. When the modem having multiple functions operates in a voice function, however, an internal reset command is not generated, and consequently, power must be applied to the modem again or the computer must be rebooted in order to reset the modem for different modem functions at different data transfer rates. It has been my observation that longer time is necessary to reset a modem having multiple modem functions. Moreover, the modem of this type can only be reset by way of the computer. Thus, if the computer is malfunctioned, the modem can not be rapidly changed into a basic modem mode for the exchange of digital data. The computer must be re-started by warm or cold booting in order that the modem is reset to be set in the basic modem mode. If the computer is operating normally, however, the user must operate the computer in accordance with a reversely setting sequence of an additional modem function in order that the modem is changed from any one of additional modem functions to a basic modem mode. As a result, the modem cannot be rapidly restored from any additional modem mode into a basic modem mode.